Fiber-reinforced thermoplastic resin molded articles comprising carbon fibers and a thermoplastic resin are excellent in terms of specific strength and specific stiffness. Thus, they are widely used in electric/electronic applications, civil engineering and building applications, automobile applications, airplane applications, and the like.
In general, in order to improve mechanical properties, continuous carbon fibers are used in fiber-reinforced thermoplastic resin molded articles in some cases. On the other hand, in some cases, moldability deteriorates, and thus it is difficult to produce fiber-reinforced thermoplastic resin molded articles having complicated shapes. Thus, discontinuous carbon fibers are preferably used to produce fiber-reinforced thermoplastic resin molded articles having complicated shapes.
For instance, a fiber-reinforced thermoplastic resin molded article in which reed-shaped pieces comprising a resin impregnated with carbon fiber bundles are arranged in a random direction has been suggested as a means of improving the mechanical properties and isotropy of such a fiber-reinforced thermoplastic resin molded article (see JP Patent No. 2507565 (page 4, line 18)). However, the presence of bundles of carbon fibers in a fiber-reinforced thermoplastic resin molded article results in generation of a resin-rich portion consisting of a resin in gaps between carbon fiber bundles, and this might cause a decrease in mechanical properties.
In addition, a thermoplastic resin molded article obtained by subjecting a stampable sheet comprising converged discontinuous carbon fibers and thermoplastic resin fibers to compression molding has been suggested (see JP Patent Publication (Kokai) No. 2002-212311 A (page 2, line 21)). However, the high melt viscosity of thermoplastic resin makes it impossible for a thermoplastic resin to impregnate converged carbon fiber bundles. Thus, non-impregnated portions are generated, and this might cause a decrease in mechanical properties.
Thus, a thermoplastic resin molded article obtained by subjecting a molding material comprising monofilamentous discontinuous carbon fibers (in a high volume content) and a thermoplastic resin powder to compression molding has been suggested (see JP Patent No. 1761874 (page 1, line 2)). However, such a molding material comprising discontinuous reinforcing fibers and thermoplastic resin particles is problematic in terms of poor handleability. This is because thermoplastic resin particles are detached from such a molding material in a step of producing a molding material, and particularly in a step of transferring a molding material, or in a step of producing a fiber-reinforced thermoplastic resin molded article, and particularly in a step of transferring and handling a molding material.
In addition, a fiber-reinforced thermoplastic resin molded article having high mechanical properties obtained by subjecting a fiber-reinforced resin sheet material obtained from uniformly dispersed carbon fibers and a thermoplastic resin to heat molding has been suggested (see JP Patent Publication (Kokai) No. 6-99431 A (1994) (page 2, line 50)). However, in such case, a fiber-reinforced resin sheet material becomes fluid in a step of subjecting a fiber-reinforced resin sheet material to heat molding, and thus carbon fibers are arranged in the flow direction of the fluid material, resulting in deterioration in isotropy as a mechanical property.